1. Field of the Invention
The present invention relates to a piezoelectric transformer and, more particularly, to a structure of a piezoelectric transformer which employs a rotated Y-cut substrate of a piezoelectric single crystal, e.g., a, single crystal of lithium niobate (LiNbO.sub.3), which enables a large load current to flow therein and possesses a high stability in operation.
2. Description of the Related Art
There are various electrical appliances requiring a high voltage of five or six kilovolts or more, e.g., for deflection of an electron beam in a cathode ray tube (CRT), for electrification of a photoconductive drum in an electrostatic printing, in a transformer for a direct current (DC) converter, and the like. To supply the high voltage, electromagnetic transformers are generally employed at present. With a recent demand for small size and light weight, however, a piezoelectric transformer has been developed as a solid state device and some piezoelectric transformers have been concretely proposed.
As an example of the proposed ones, a piezoelectric transformer is known which employs a ceramic substrate having an input portion polarized in a certain direction and an output portion polarized in another direction. In this piezoelectric transformer, however, a problem occurs in that, where an excited vibration is greatly displaced, a distortion is concentrated on the portion where the direction of the polarization is changed, and thereby the substrate is broken or destroyed.
Also, since ceramic material generally presents its saturation characteristics and as an input voltage applied thereto is increased, a drawback arises in that the piezoelectric constants and elastic constants are deteriorated due to the emitted heat or other causes. This results in a lowering in stability or reliability in operation of the piezoelectric transformer.
Note, the problems in the prior art will be explained in detail later in contrast with the preferred embodiments of the present invention.